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Publication numberUS2760431 A
Publication typeGrant
Publication dateAug 28, 1956
Filing dateJun 19, 1952
Priority dateJun 19, 1952
Publication numberUS 2760431 A, US 2760431A, US-A-2760431, US2760431 A, US2760431A
InventorsJulian L Beatty
Original AssigneeDick Co Ab
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Lithographic plates and methods for manufacturing same
US 2760431 A
Abstract  available in
Images(5)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Ofiice Patented Aug. 28, 1956 LITHOGRAPHIC PLATES .AND METHODS FOR MANUFACTURING SAME Julian L. Beatty, Northbrook, 11]., assignor to Dick Company, Niles, 11]., a corporation of Illinois No Drawing. Application June 19, 1952, Serial No. 294,489

11 Claims. (Cl. 101--1'49.2)

.it relates more particularly to the manufacture of a lithographic plate for use in the reproduction of copies .by lithographic technique. I In accordance with the present pract1ce, rn the manufacture of a lithographic surface on a suitable carrier,

such as paper, for use in oifice copy duplication or the like, it is necessary to make several applications ofcoating materials to the surface of the paper before the desired lithographic properties are developed. "In the simplest lithographic plate manufactured at the present time, a coating formulated of a material such as casein and ester gum is applied to the paper in order to function as a base for the Water receptive hydrophilic colloid. The colloid composition formulated of such materials as clay, casein and other filler-s with formaldehyde is applied in one or more layers onto the base coat, depending upon the length of run desired of the plate. After the colloid coating has dried, the surface is insolubilized with a wash coat of a polyvalent metal, such as a solution of aluminum chloride, Zinc chloride, aluminum formate or the like and then insensitized with a coating of sodium silicate or a hydrophilic colloid coat such as of albumen, alginate, guar gum or the like.

In the event that a long run plate is desired, the paper base sheet is usually pretreated to render it substantially Water repellent as by the application of a resinous varnish, such as a phenol formaldehyde varnish, urea formaldehyde solution, melamine formaldehyde solution or the like. The surfaces of the treated paper become less receptive to the hydrophilic coatings and, unless an intermediate anchoring coat is applied to the surface, a satisfactory bonding relation may not be established with the fibrous base sheet. Thus as many as 5 to 7 or more coatings are employed to produce a suitable lithographic surface on paper or the like.

It is an object of this invention to produce and to provide a method for producing a new and improved lithographic surface.

Another object is to produce and to provide a method for producing a lithographic plate of the type described which requires considerably fewer operational steps 1n its manufacture and markedly less material and which in operation is capable of supplying copy of good quality substantially immediately.

A further object is to produce a low cost lithographic plate of the type described which is easy to manufacture and which becomes insensitive without the requirement of special treatments and it is a related object to produce a lithographic plate of the type described in a single coating process to provide considerable savings in time, labor and material; which is characterized by excellent stability, substantial insensitivity and which is capable of holding an ink receptive image having the properties of immediate reproduction of copy of good quality, and which continues to produce such copies for a considerable length of time.

In accordance with the practice of this invention, a lithographic surface of the type described may be produced in a singlecoating with a composition containing ammonia, a Water soluble polyacrylic acid and an inert filler in finely divided form in combinationwith an oxide or a hydroxide of a polyvalent metal capable of form ing an insoluble salt with the polyacrylic acid but which remains soluble in the presence of sufiicient ammonia in the form of ammonium hydroxide 'or a water soluble ammonia salt.

For a better understanding of this invention, description will now be made of the manufacture of a medium run lithographic plate embodying features Oflhi's invention, but it will be understood that the following examples are given 'by way of illustration and not by way of limitation:

Example 1 180 parts by weight finely divided clay and 18 parts by Weight zinc oxide in "finely divided form are mixed and formed into a slurry with about parts by weight water. In a separate container, parts 'by Weight of a 25 percent water solution of polyacrylic acid (Polyco 437, manufactured by American Polymer Company, or Acrysol CH144C, manufactured by Rohm & Haas) is neutralized With about 100 parts by Weight concentrated ammonium hydroxide and then the polyacrylic acid solution is combined with the slurry of clay and zinc oxide. This forms a relatively stable coating composition con taining about 40 percent solids.

The composition is coated onto a high wet strength paper in coating weights of about 8-10 pounds per 3000 square feet of surface and then the coating may be allowed to air dry but it is preferably dried at an elevated temperature, such as a temperature within the range of ZOO-350 F. to accelerate the drying rate. The coating may be applied by a brush .coater, roller coater, or knife coater, but it is preferred to use an air knife applicator in order to achieve greater uniformity in coating weights and a smoother coated surface. Upon drying, the hydrophilic colloid material becomes highly insoluble possibly by reason of the fact that the ammonia ion is eliminated by volatilization with the result that an insoluble metal salt with the polyacrylate is formed.

The resulting surface is highly receptive to water so that it is substantially immediately Wet out with repellent. in use, yet it is capable of receiving and holding an ink receptive, water repellent imaging material applied by various means common in the imaging of conventional lithographic surfaces.

The lithographic surface that is formed on the paper base sheet does not cause excessive stiffening or embrittlement of the base sheet so that the composite structure can be readily used in a typewriter or the like for imaging in the usual manner for office duplication. Although the surface formed upon drying of the coating composition is insoluble yet readily wet out by Water or other repellent in the non-imaging areas and Water repellent and ink receptive in the areas imaged with a greasy composition or the like, the surface is sufficiently insensitive without further treatment to resist reproduction of areas which might giadvertently be touched as an incidence to normal harring.

In the finger print test developed specifically to insure sensitivity of the surface, a finger upon which skin oils 3 out subsequent treatment and without any special haudling to insensitize the surface produces copy completely free of finger print smears or reproduction.

Another important improvement existing in lithographic surfaces prepared in accordance with this invention resides in the ability to produce copy of good quality immediately on the first copy sheet passed through the machine as compared to the necessity to Waste up to 10 sheets or more before copy of good quality is produced in many of the plates embodying more complicated systems. This ability immediately to produce copy is of considerable importance where runs of about 25 to 100 copies are desired. Where thousands of copies are to be produced, the loss of the first 5 or sheets if of lesser consequence.

The amount of zinc oxide in the coating composition is preferably maintained within the range of 2 parts by weight zinc oxide to 47 parts by weight of the polyacrylic acid. When lesser amounts of zinc oxide are used the formed surface appears to be less capable of resisting deterioration in use. When higher concentrations of zinc oxide are employed, the coating that is formed becomes brittle but greater amounts can be used when the coating composition is modified to include flexibilizing agents such as glycerine, ethylene glycol, polyethylene glycol and other polyhydric alcohols. Under any circumstances, it is not desirable to use zinc oxide in amounts in excess of the concentration of polyacrylic acid.

To the present, best use is made of zinc oxide as a component of the filler system, but similar results with respect to the solibility of the acrylic acid in the presence of sufiicient ammonia and insolubilization of the polyacrylate upon loss of ammonia from the coating composition have been found to result from the use of zinc hydroxide in equivalent amounts on the molecular Weight basis. Though the coating appears to be somewhat more tacky, zinc oxide may be replaced by magnesium oxide or hydroxide and to a lesser extent by other alkaline earth metal oxides or hydroxides of the type calcium oxide, lead oxide and barium oxide.

As previously pointed out, instead of concentrated solutions of ammonium hydroxide, it has been found that use may be made of other Water soluble salts of ammonia capable of freeing the ammonia ion in amounts suflicient to maintain the solubility of the polyacrylic acid in the presence of the metal oyides or hydroxides.

The exact phenomenon which occurs in a system of the type described has not been fully determined. It is possible that the ammonium ion maintains the solubility of the polyacrylic acid for formation of a complex double salt therewith in combination with a metallic component whereby the materials are maintained in solution in the composition but an insolubilized salt is formed upon release of ammonia during drying. It is also possible that the salt forming group of the polyacrylic acid is preferentially receptlve to the ammoma 10H to resist combination with the metallic ion in the formation .of the insoluble salt or it may be that the ammonium ion forms an insoluble salt with the metallic oxide or hydroxide having characteristics which militate against the formation of an insoluble salt with the polyacrylic acid.

Instead of clay, other inert fillers such as diatomaceous earth, satin white, chalk, talc, silica and the like in substantially equivalent amounts may be used. Best results are secured when the ratio of inert filler to metal oxide is maintained within the range of 1 part by weight metal oxide or its equivalent weight of hydroxide to 2-20 parts by weight filler and when the ratio of filler and metal oxide or hydroxide to polyacrylic acid is maintained within the range of 1 part by weight polyacrylic acid to 2-10 parts by weight of the filler and metal oxide.

While description has been made of a system wherein ammonia is present in amounts sufficient to maintain the solubliity of the polyacrylic acid in the presence of metal oxide, the amount for solubilization defines the minimum concentration thereof. Larger amounts of ammonia can be used further to increase the stability of the composition and larger amounts of ammonia are often preferred to lower the apparent viscosity of the coating composition to achieve heavier coating Weights. Instead of ammonium hydroxide, use may be made of ammonium carbonate or the like in equivalent amounts on a molecular weight basis.

The solids content of the coating composition may be varied over a fairly wide range, such as from 20 to 60 percent, depending upon the manner of application and the coating weight desired on the base sheet. Coating weights of 6 to 12 pounds per 3000 square feet of surface are capable of being secured by a single application to provide a lithographic surface suitable for use in the reproduction of up to 1000 or more copies. While it is preferred to rely on a single coating step in the manufacture of a low cost lithographic plate, multiple coatings may be applied when desired to achieve heavier coating weights and longer life in use for the reproduction of copies.

Suitable supports for the lithographic surface may include paper, fiber board, textile fabrics, plastic sheet stock or metal strip preferably of such thin dimension as to provide for sufiicient flexibility for bending about a typewriter platen but with sufiicient strength to maintain dimensional stability for at least the number of copies that is desired to produce therefrom. When a fairly large number of copies are desired and when the base sheet comprises paper or other sheet stock of fibrous character ordinarily having a high degree of water absorption, it is desirable to introduce high wet strength into the base fabric by pretreatment with water repellent materials such as resinous solutions of urea formaldehyde, melamine formaldehyde, phenol formaldehyde or alkyd resins, or by treatment of the fabric with wax, oils, fatty acid amines or other water repellent surfaces.

Further examples of the practice of this invention are as follows:

Example 2 Coating composition:

160 parts polyacrylic acid, 25% solids parts ammonium hydroxide, concentrated solution parts clay 30 parts zinc hydroxide Example 3 Coating composition:

parts polyacrylic acid, 25% solids 150 parts ammonium carbonate parts clay 30 parts zinc oxide Example 4 Coating composition:

160 parts polyacrylic acid, 25 solids 100 parts concentrated ammonium hydroxide 80 parts satin white 100 parts clay 15 parts zinc oxide Example 5 Coating composition:

160 parts polyacrylic acid 130 parts ammonium hydroxide 180 parts clay 20 parts magnesium oxide The above compositions, diluted with water to a solids content ranging from 40-60 per cent solids, may be applied as by an air blade applicator in amounts to provide a coating weight of 6-12 pounds per 3000 square feet of surface onto 40-pound high wet strength kraft paper. The coated paper may immediately be passed through an air drying oven heated to a temperature of about 250 F. whereupon the coating becomes substantially completely insolubilized to provide alithographic surface of the type described.

It has been found that insolubility of the coating and the life of the lithographic surface is further improved by the addition of water soluble bivalent metal salts of the type zinc chloride and zinc acetate to the coating composition. Incorporation may'be made by introduction of the zinc salt as an ingredient in the coating composition in amounts ranging from 1-10 per cent by weight thereof. While it is preferred to incorporate the bivalent metal salt as an ingredient in the coating composition to provide a single coating process for the manufacture of lithographic plates, improved results may also be secured when the bivalent metal salt is applied as a wash coat on the formed surface. Such application may be made from solutions containing the bivalent metal salt in amounts ranging from 5-25 per cent by weight. Instead of zinc salts of the type described, use may also be made of the water solublesalts of magnesium, nickel, cobalt, calcium, barium andthe like in the form of their chlorides, acetates and the like.

Example 6 160 parts polyacrylic acid, 25% solids 120 parts ammonium hydroxide, concentrated 180 parts clay 15 parts Zinc oxide 5 parts zinc chloride The above composition may be applied onto a suitable base sheet in the manner previously described with respect to Examples 1-5 inclusive. Brushing the surface of the plate while wet but preferably while dry, as with a bristle brush, soft cotton pad or the like improves the lithographic properties of the plate, as by making correction easier, improving wet-out and decreasing penetration of repellent or moisture into the coating.

As previously pointed out, the hydrophilic lithographic surface formed of clay-zine polyacrylate in accordance with the practice of this invention may be formed on a surface previously coated with an insolubilized hydrophilic colloid. This modification to produce an excellent lithographic plate capable of immediate reproduction and long life may be illustrated by the following.

Example 7 Coating composition:

66.0 per cent clay 22.0 per cent zinc caseinate 11.0 per cent satin white 0.8 per cent ammonia 0.2 per cent formaldehyde (30% formalin) Water is added to the above ingredients in sufficient amounts to reduce the viscosity to that suitable for brush coating. Coating compositions to provide coating weights of about 14 pounds per 500 of 20 by 24 inch plates are applied to the surface of high wet strength paper in the form of a continuous web followed by drying at elevated temperature of about 250 F.

After the colloid coating has dried, it is further treated by the application of a wash coat containing 86 per cent by weight aluminum formate and 14 per cent by weight butanol. The wash coat is applied in amounts of about 1.5 gallons per 500 sheets and then air dried or dried at elevated temperature by running through an air drying oven or in a festoon drier.

Thereafter, anyone of the compositions of Examples 1-6 may be applied in the manner described to produce The diazolith compound may be applied onto a zinc polyacrylate coating. formed directly on a base sheet, as in Examples 1-6, or onto a lithographic coating formed on an insolubilized hydrophilic coating, as in Example 7.

The following examples will illustrate the production of presensitizedphotolithographic plates embodying few turesof this invention:

Example 8 A sensitizing solution containing 1 percent by weight Diazolith #1 compound, marketed by Edwal Laboratories, 5 percent sodium acetate and 94- percent water is swabbed onto any of the surfaces prepared in accordance with Examples l-7 inclusive.

Lithographic surfaces formed of zinc or other of the described polyacrylate compositions directly on a base sheet or upon an insolubilized hydrophilic colloid coating may also be presensitized with a diazolith compound to" produce a presensitized photolithographic plate. The following will specifically illustrate the manufacture of presensitized plates of the type described on zinc polyacrylate surfaces.

Example 9 A- supercalendered kraft paper is rod coated with the following composition:

25 parts by weight zinc chloride 25" parts by weight water parts by weight ammonium hydroxide in solution 100 parts by weigh polyacrylic acid (Polyco 437--Americ'an Polymer Company) The coating composition is prepared by dissolving the zinc chloride in water, adding the ammonium hydroxide and then incorporating the polyacrylic acid. The coating composition is applied to the paper base sheet in amount to provide coating weights of 20-30 pounds per 3000 square feet of surface area. When dry, the surface is swabbed with a 1 percent solution of the diazolith compound corresponding to that produced by Example 1 of the Schmidt Patent No. 2,063,631. The diazolith is incorporated with 4 percent sodium acetate in water solu-- tion. The plate formed with the above composition need not be desensitized after exposure and before running to produce copies.

Example 10 High wet strength kraft paper is coated first with a composition containing the following:

Colloid base coat composition:

6 1 percent clay 20 percent zinc caseinate 18 percent satin white 0.8 percent ammonium hydroxide 0.2 percent formaldehyde The colloid composition is brush coated onto a web of high strength paper to provide a coating weight of 30 pounds per 3000 square feet of surface area. After the coating has been dried as in a festoon drier at a temperature between 200 and 300 F., the surface is washed with a 65 percent solution of aluminum formate.

Lithographic coating composition: 10 grams sodium polyacrylate 10 grams zinc chloride 45 milliliters concentrated ammonium hydroxide face is brushed with bristle brushes and after the surface has been dried, preferably at elevated temperature, it is swabbed with a solution containing 1 percent Diazolith #1, marketed by Edwal Laboratories, percent sodium acetate and 94 percent Water. The applied solution is adjusted to a pH of about 6.3.

While it is preferred to use the diazolith compounds of the type described as the presensitizing composition for lithographic surfaces formed in accordance with the practice of this invention, it will be understood that other conventional sensitizing agents may also be used.

It will be further understood that various changes may be made in the formulations with respect to the ingredients and their manner of incorporation and in the steps of applying the coating composition onto the base sheet without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A planographic printing plate comprising a base sheet and a continuous, water insoluble lithographic surface layer on the base sheet in the form of a coating comprising the reaction product of the combination in admixture of an inert filler, polyacrylic acid and zinc oxide and an ink receptive, water repellent, hydrophobic imaging material in the form of a mechanically applied image anchored onto the underlying continuous, Water insoluble surface layer.

2. A planographic printing plate comprising a base sheet and a continuous, water insoluble lithographic surface layer on the base sheet in the form of a coating comprising the reaction product of the combination in admixture of an inert filler, polyacrylic acid and zinc oxide present in the ratio of 2 parts by weight thereof to 4 to 7 parts by Weight of the polyacrylic acid and an ink receptive, water repellent, hydrophobic imaging material in the form of a mechanically applied image anchored onto the underlying continuous, water insoluble lithographic surface layer.

3. A planographic printing plate comprising a base sheet and a continuous, water insoluble lithographic surface layer on the base sheet in the form of a coating comprising the reaction product of the combination in admixture of an inert filler, polyacrylic acid and zinc oxide present in the ratio of 1 part by weight thereof to 2 to 20 parts by Weight of the filler and 1 part by Weight polyacrylic acid to 2 to 10 parts by Weight of the filler plus base and an ink receptive, Water repellent, hydrophobic imaging material in the form of a mechanically applied image anchored onto the underlying continuous, water insoluble lithographic surface layer.

4. A planographic printing plate comprising a base sheet and a continuous, water insoluble lithographic surface layer on the base sheet in the form of a coating comprising the reaction product of the combination in admixture of an inert filler, polyacrylic acid and a bivalent metal salt which forms a water insoluble polyacrylate and a water soluble, water stable complex double salt with the polyacrylate in the presence of suflicient ammonia and present in the ratio of 1 part by weight of the metal salt to 2 to parts by weight filler and 1 part by weight polyacrylic acid to 2 to 10 parts by weight of the filler plus metal salt and an ink receptive, Water repellent, hydrophobic imaging material in the form of a mechanically applied image anchored onto the underlying continuous, water insoluble lithographic surface layer.

5. A planographic printing plate comprising a base sheet and a continuous, water insoluble lithographic surface layer on the base sheet in the form of a coating comprising the reaction product of the combination in admixture of an inert filler, polyacrylic acid and a metal base selected from the group consisting of the oxides and hydroxides of zinc, magnesium, calcium, lead and barium and mixtures thereof and present in the ratio of 1 part by weight of the metal base to 2 to 20 parts by Weight of the filler and 1 part by Weight polyacrylic acid to 2 to 10 parts by weight of filler and metal base and an ink receptive, water repellent, hydrophobic imaging material in the form of a mechanically applied image anchored onto the underlying continuous, Water insoluble lithographic surface layer.

6. The method of manufacturing a planographic printing plate comprising the steps of coating a base sheet to provide a continuous lithographic surface layer with a composition containing inert filler, polyacrylic acid, a water soluble bivalent metal salt which forms a water insoluble polyacrylate and a Water soluble, water stable complex double salt with the polyacrylate in the presence of sufficient ammonia and present in the ratio of 1 part by weight metal salt to 2 to 20 parts by weight filler and 1 part by weight polyacrylic acid to 2 to 10 parts by Weight filler plus metal salt and sufficient ammonium ion present in the composition to maintain the metal salt and polyacrylic acid in solution, and drying the coating on the base sheet to form a hydrophilic, lithographic surface which becomes Water insoluble upon elimination of ammonia and mechanically applying to said continuous lithographic surface layer an image in the form of a water repellent, hydrophobic, ink receptive material.

7. The method of manufacturing a planographic printing plate comprising the steps of coating :1 base sheet to provide a continuous lithographic surface layer with a composition containing inert filler, polyacrylic acid and a metal base selected from the group consisting of the oxides and hydroxides of zinc, magnesium, calcium, lead and barium and mixtures thereof and sufficient ammonium ion present to maintain the metal base and polyacrylic acid in solution, and drying the coating on the base sheet to form a hydrophilic, lithographic surface which becomes water insoluble upon elimination of ammonia and mechanically applying to said continuous lithographic surface layer an image in the form of a water repellent, hydrophobic, ink receptive material.

8. The method of manufacturing a planographic printing plate comprising the steps of coating a base sheet to provide a continuous lithographic surface layer with a composition containing inert filler, polyacrylic acid, a zinc base selected from the group consisting of zinc oxide, zinc hydroxide and mixtures thereof and present in the ratio of 1 part by weight zinc base to 2 to 20 parts by weight filler and 1 part by weight polyacrylic acid to 2 to 10 parts by weight filler plus zinc base and ammonium ion present in amounts in excess of that necessary to maintain the solubility of the zinc base and the polyacrylic acid, and drying the coating to form a continuous, water insoluble hydrophilic, lithographic surface layer, and mechanically applying to said continuous lithographic surface layer an image in the form of a water repellent, hydrophobic, ink receptive material 9. The method of manufacturing a planographic printing plate comprising the steps of coating a base sheet to provide a continuous lithographic surface layer with a composition containing inert filler, polyacrylic acid, and a metal base selected from the group consisting of the oxides and hydroxides of zinc, magnesium, calcium, lead and barium and mixtures thereof and present in the ratio of 1 part by weight metal base to 2 to 20 parts by weight filler and 1 part by Weight polyacrylic acid to 2 to 10 parts by weight filler plus metal base and ammonium ion present in amounts in excess of that necessary to maintain the solubility of the metal base and the polyacrylic acid, drying the coating to form a continuous, water insoluble hydrophilic, lithographic surface layer and mechanically applying to said continuous lithographic surface layer an image in the form of a water repellent, hydrophobic, ink receptive material.

10. The method of manufacturing a planographic printing plate as claimed in claim 7 which includes the additional step of Wash coating the dried lithographic surface with a solution of a bivalent metal salt.

ll. The method of manufacturing a panographic printing plate as claimed in claim 8 which includes the addi- 10 tional step of Wash coating the dried lithographic surface FOREIGN PATENTS with a solution of a bivalent metal salt. 371,041 Great Britain of 1932 References Cited in the file of this patent THE REFERENCES UNITED STATES PATENTS 5 Ser. No. 397,138, Fikentscher et al. (A. P. C.), pub- 1,981,102 Hagedorn et a1. Nov. 20, 1934 hshed May 1943- 2,184,310 Meigs et a1. Dec. 26, 1939 2,649,373 Neugebauer et a1 Aug. 18, 1953

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2922715 *Mar 26, 1956Jan 26, 1960Polychrome CorpPresensitized printing plate and method for preparing same
US2951441 *Jan 16, 1956Sep 6, 1960Timefax CorpLithographic printing plates and coatings therefor
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Classifications
U.S. Classification101/457, 524/432, 524/433, 524/430, 101/462, 524/434, 101/466, 430/935, 430/302
International ClassificationB41N3/03
Cooperative ClassificationY10S430/136, B41C1/1091, B41N3/036
European ClassificationB41N3/03P, B41C1/10T